That Enhances Ammonia Production Through Nitrogen Fixation

Dr. Thet Swe Zan, a postdoctoral researcher and first author, along with Research Professor Jong Cho-Eun (corresponding author), Professor Choi Eun-Ha (Director of PRBC), and Professor Yoon Yeo-Min (Ewha Womans University), all from Professor Jang Min's research team (Department of Environmental Engineering, Kwangwoon University), have successfully developed a Ruthenium (Ru)-doped Bismuth Titanate photocatalyst that significantly enhances ammonia production without requiring sacrificial reagents.

Ammonia is a key industrial chemical primarily used in fertilizer production and as an energy storage material that can be converted into hydrogen. It is typically synthesized through the Haber-Bosch process, which involves combining nitrogen and hydrogen under high pressure and high temperature in the presence of a catalyst. However, the Haber-Bosch process is highly energy-intensive and heavily reliant on fossil fuels to produce the necessary hydrogen, resulting in significant greenhouse gas emissions. With the global demand for ammonia rising exponentially, there is an urgent need to develop more sustainable production methods.

Photocatalytic nitrogen fixation, which converts atmospheric nitrogen and water into ammonia using sunlight as an energy source, is an emerging technology with significant potential. While it is more environmentally friendly compared to the conventional Haber-Bosch process, substantial research and development are still required to optimize the efficiency, scalability, and economic feasibility of photocatalytic ammonia synthesis. Sacrificial reagents, such as methanol or ethanol, are effective in increasing ammonia yield through photocatalytic nitrogen fixation but come with the drawback of higher operating costs.

Bismuth titanate (Bi₄Ti₃O₁2) has a bandgap structure suitable for photocatalytic nitrogen fixation to produce ammonia. However, it has limitations due to restricted separation of photoexcited electron-hole pairs, weak interactions with N₂, and a tendency to favor hydrogen evolution reaction (HER), which hinders its efficiency. In response, Professor Jang Min’s research team developed a Ruthenium (Ru)-doped Bi₄Ti₃O₁2 photocatalyst aimed at enhancing the interaction between N₂ molecules and active sites on the photocatalyst surface to produce ammonia without the use of sacrificial reagents. The ammonia production rate of the Ru-Bi₄Ti₃O₁2 photocatalyst was 3.2 times higher than that of the pure Bi4Ti3O12 photocatalyst. In the absence of sacrificial reagents, a novel result was observed in which ammonia formation occurred through the oxidation of N₂ into NO_x species at the valence band of the photocatalyst, followed by the photo-reduction of NOx species at the conduction band to produce ammonia. This mechanism was further validated using in-situ SERS Raman and time-lapse FTIR analyses, which demonstrated that Ru doping enhances the interaction between N₂ molecules and Bi sites, facilitating N₂ photo-oxidation.

 [Principle of Nitrogen Fixation and Ammonia Production by Ru-Doped Bi₄Ti₃O₁2 Photocatalyst]

This study was published in the journal Applied Surface Science (JCR Impact Factor 6.3, ranked first in the field of Materials Science (Coatings and Films), JCR percentile: 97.83%). It was supported by research funding from the National Research Foundation of Korea (NRF) under the Ministry of Education (RS-2023-00240726, RS-2023-00282898, 2021R1A6A1A03038785, and 2023R1A2C1003464).

https://www.sciencedirect.com/science/article/abs/pii/S0169433224026060

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